Visual detection of cyanobacterial hepatotoxins by thin-layer chromatography and application to water analysis

Visualization reactions for the thin-layer chromatographic (TLC) analysis of cyanobacterial hepatotoxins microcystins and nodularin were studied. Of the 17 potential reactions tested, nine yielded either coloured, fluorescent, or both products with the purified toxins. The detection limit of pure microcystin-LR in these reactions ranged from 10 to 250 ng. Feasibility of the reactions for water analysis was studied in fortified 50–500 ml water samples. The best result was obtained with N,N-dimethyl-1,4-phenylendiammonium dichloride (N,N-DPDD). A water analysis method meeting the WHO drinking water guideline concentration value, 1 μg/l of microcystin-LR, was developed employing N,N-DPDD. The method was tested by analyzing blind 38 authentic natural water samples, studied earlier by the enzyme-linked immunosorbent assay (ELISA) and protein phosphatase inhibition assay (PP). In 31 samples the results of all three methods were consistent. Two apparently false positive results were obtained by TLC, and in two samples results were positive by ELISA and TLC but not PP. In one sample the result was positive by PP but not ELISA or TLC. Two samples were positive by ELISA and PP and not TLC, but a full 50 ml sample for TLC was not available in these cases, thus making the detection limit higher. Results suggest that the present TLC method is comparable with the ELISA and PP assays, and TLC can be used for cost-effective monitoring of water samples according to the WHO guidelines.